This invention relates generally to marine propulsion devices, such as outboard motors and stern drive units, including a vertically tiltable propulsion assembly supporting a propeller. More particularly, this invention relates to means for controlling the trim and tilt systems of such marine propulsion devices.
Marine propulsion devices typically include one or more hydraulically actuated cylinders for vertically trimming and/or tilting a lower unit carrying a propeller to desired angular positions. Operation of these cylinders usually is controlled by a manually operable switch which is movable between three positions, neutral or "off", "up" and "down". The switch is operated to trim the propeller position during boat operation. Trimming is carried out over a range of positions from a full down position to an upper limit of approximately 10.degree.-15.degree. above the full down position. This changes the angle of propeller thrust which causes the boat to raise or lower, thereby enabling selection of the proper and/or most efficient propeller thrust angle for different loads, different water conditions and boat planing. The lower unit is tilted or raised above the trim range into the tilt range to insure clearance when boating in shallow water and facilitate launching or trailering.
When separate hydraulic cylinders are used to perform the trim and tilt functions, the actuation system for each can be selectively hydraulically isolated to prevent actuation of the tilt cylinder(s) while operating at relatively high engine speeds and thereby prevent potentially harmful engine overspeeding under low load or no load conditions. When a single hydraulic cylinder and/or a plurality of hydraulic cylinders acting in parallel is used to provide both trimming and tilting, the operation of the cylinder(s) in the trim and tilt ranges has not been hydraulically separated, so a different type of control is required.
Examples of prior art trim and/or tilt controls are disclosed in the following U.S. patents:
______________________________________ Patentee U.S. Pat. No. Issue Date ______________________________________ Mettelal 3,406,652 October 22,1968 North 3,434,449 March 25, 1969 Moberg 3,581,702 June 1, 1971 Carpenter 3,722,455 March 27, 1973 Hager 3,834,345 September 10, 1974 Borst 3,863,592 February 4, 1975 Borst 3,885,517 May 27, 1975 Hager 3,894,250 July 8, 1975 Hall 4,064,824 December 27, 1977 Hall 4,096,820 June 27, 1978 Pitchford 4,318,699 March 9, 1982 Hall 4,373,921 February 15, 1983 Cavil 4,413,215 November 1, 1983 ______________________________________
None of these patents describes a simple means for controlling the operation of a hydraulic cylinder(s) which performs both the trim and tilt functions so that the propulsion assembly can not be raised from a trim position to a tilt position under high propeller thrust conditions and is automatically returned from a tilt position to a trim position under high propeller thrust conditions.